The invention generally relates to wireless hybrid time division multiple access/code division multiple access communication systems. In particular, the invention relates to resource management in such systems.
FIG. 1 depicts a physical layout of a wireless communication system. The system has a plurality of base stations 20. Each base station 20 communicates with user equipments (UEs) 22 in its operating area or cell 23. Communications transmitted from the base stations 20 to the UEs 22 are referred to as downlink communications and communications transmitted from the UEs 22 to the base stations 20 are referred to as uplink communications.
A network perspective of a wireless communication system is shown in FIG. 2. Each node-B 24 within the system wirelessly communicates with associated UEs 22 or users. Each node-B 24 has a single site controller (SC) 34 associated with either a single or multiple base stations 20. A group of node-Bs 24 is connected to a radio network controller (RNC) 281. To transfer communications between RNCs 28, an interface between the RNCs (IUR) 26 is utilized. Each RNC 28 is connected to a mobile switching center (MSC) 30 which in turn is connected to the core network 32.
In code division multiple access (CDMA) communication systems, multiple communications can be sent over the same spectrum simultaneously. The multiple communications are distinguished by their codes. In hybrid time division multiple access (TDMA)/CDMA communication systems, such as time division duplex (TDD) using CDMA (TDD/CDMA) communication systems, the spectrum is time divided into repeating frames having time slots, such as fifteen time slots. In such systems, communications are sent in selected time slots using selected codes. A physical channel is defined as one code in one time slot. The use of a single code in a single time slot with a spreading factor of sixteen is referred to as a resource unit. Based on the type of service being provided to a user (UE 22) in the system, one or multiple physical channels may be assigned to support the users uplink and downlink communications.
The assignment of physical channels to users in such a system is a complex problem. Each physical channel used in a time slot creates interference with respect to other channels used in that time slot. Accordingly, it is desirable to choose time slots as to minimize interference.
However, there are drawbacks to choosing time slots solely based on interference. A UE 22 communicating using less time slots typically will have a lower power consumption. By stacking codes in a smaller number of time slots, other time slots are left open for new users. Additionally, some UEs 22 may be only able to use a few time slots, such as one or two.
Accordingly, it is desirable to have effective resource management in hybrid TDMA/CDMA communication systems.